1) Field of the Invention
The present invention relates to a picture producing apparatus which is capable of converting and processing picture information signals obtained from an original picture, and producing a reproduced picture having an excellent reproducibility in tone in a novel tonal conversion system.
More particularly, the present invention concerns a picture producing apparatus which can form a reproduced picture having an excellent reproducibility in tone and color-tone on a recording sheet by obtaining genuine picture information values from an original picture, and converting and processing the obtained values in a tonal adjustment system, using a specific tonal conversion, upon producing a reproduced picture from one of various types of pictures. In this invention, any objects can be an original picture as far as it is desired to be reproduced on a recording sheet. It should be noted that the original pictures include not only usual original pictures, for example, photographic pictures in monochromatic color or in multiple color, and video signal (TV) pictures, but also subjects or objects to be shot such as still lives, human figures or the like, which can become bases of the original pictures, when producing reproduced pictures in accordance with the present invention.
Further specifically, the present invention concerns an entirely novel picture producing apparatus provided with a tone adjusting system, where, upon producing a reproduced picture from an original picture, picture information values for the reproduced picture are obtained by recording, storing or processing them on an input medium for picture information (for example, photographic material or photoelectric transfer device such as two-dimensional CCD, photomultiplier, photodiode, CCD, or the like is used as the input medium; hereinafter it is referred as "recording medium" collectively), that is, obtained are picture information values correlating to light intensity inputted to such a recording medium for producing a medium image from an original picture, not picture information values correlating to density from a medium image as in conventional manners, and converting and processing such picture information values, by using a specific tonal conversion formula. In the present invention, a picture stored on such a recording media is called as "a medium picture recorded on a recording medium" or merely as "a medium image", in contrast to the term "an original picture".
2) Description of the Related Art
In the case of reproduction of a picture from an original picture having a continuous tone such as a photograph, the picture having a continuous tone corresponding to the original picture is formed (silver salt photographic recording) by subjecting the original picture to an analog process (exposing), if used sensitized paper as a recording sheet therein. On the other hand, in a printer of a various type, a copy machine, or the like (hereinafter referred as "a picture producing system", which should be interpreted in the broadest sense), which records digitally a picture on a plain paper, the picture is not formed in said analog process so that it is difficult to reproduce a gradation of the original picture. In this case, it is particularly difficult in a multi-color reproduction process to control a color-balance together with a gradation.
From the above reason, considerable efforts have been made in improvement of reproducton of tone and color-balance in various picture producing apparatus. The picture producing apparatus is adapted to form a reproduced picture in such a manner that an original picture having a continuous tone such as a photograph is photoelectrically scanned to obtain density information values, it being possible to obtain the density information values in another manner, the obtained density information values are processed and converted into signals, and, based on the signals, a picture having a tone or color-tone corresponding to that of the original picture is formed by distribution of pixels on a recording paper, as similar as in the manner for converting a continuous tone into a halftone in a photomechanical process.
However, as conventional picture producing apparatus has a non-scientific tonal control system for processing density information values obtained from an original picture in order to reproduce the gradation, it is the present condition that there are unavailable satisfactory reproducibility in gradation and color-tone, color-tone having an intimate relationship with gradation.
As well known, a gradation of the reproduced picture depends on a system adapted for representing the density of the pixels. As systems for representing a graduation of pixels, there are some such as a system where a pixel coverage rate is varied with the size of a dot (variable-area system or variable-area dot, this system being adopted in monchromatic and color scanners, ink jets of a piezoelectric type, etc.), a system where a pixel coverage rate is varied with the number of arranged dot of a fixed size (a same size) (variable-concentration system or constant dot, this system being adopted in thermal molten-ink transfer, etc.), and a system where a density of a fixed dot (every dot having the same size) itself is varied (variable-density system or variable-density dot, this system being adopted in thermal sublimation transfer).
However, the present circumstances are such that, if a reproduced picture is intended to form from an original picture in a conventional picture producing apparatus, no scientific study is given to a manner how to set a pixel coverage rate (a ratio of recorded pixels to the number of unit pixels constituting a pixel block), which is represented by a size of a dot or an intensity of a dot corresponding to a density information value of a given sample point (pixel) on the original picture, for example a pixel on a reproduced picture corresponding thereto, namely, a value defining the gradation of a pixel, and a manner how to obtain a tonal intensity value of a pixel (hereinafter referred as "tonal intensity value of pixel", or "tonal intensity value", simply, this term being used commonly in the various representing system for pixel gradation), and a manner how to obtain such a tonal intensity value to a pixel.
As having been developed no scientific formula correlating a density information value of a given pixel on the original picture with a tonal intensity value of a corresponding pixel on the reproduced picture, there is no other way but relying upon a correlation formula established by respective manufacturers, based on their previous experiences and perception, or a limited number of fixed conditions.
It is therefore extremely difficult to obtain a desired reproduced picture excellent in tone or color-tone when an original picture has a quality which is out of manufacturers' supposition, such as a non-standard color-film original (over-exposed, excessively light original; under-exposed, excessively dark original; original in high-key or low-key; color-fogged or faded original, etc.). This results in that has not been developed any flexible picture producing apparatus which can produce a reproduced picture having a desired quality from a standard original and even from a non-standard original, and desirably alter or modify (alteration and modification of tone and/or color-tone) the quality of an original picture.
It means that the conventional apparatus is incapable of scientifically and rationally converting a density information value of a given pixel on an original picture, which value is a picture information value on the original and is extremely important in production of a reproduced picture, into a tonal intensity value of a corresponding pixel on the reproduced picture.
A cause of the above problem inherited in the conventional apparatus is admitted to lie in the conception of the conversion step of gradation of a picture, which step takes an important role in the initial stage when finally producing a reproduced picture by means of a distribution of pixels from an original such as a continuous-tone picture.
It is admitted that the conventional tonal conversion technique of pictures is carried out, relying entirely on experiences and perception, not on the basis of scientific and rational techniques, when converting a density information value of a given pixel of an original picture into a tonal intensity value of a corresponding pixel on a reproduced picture.